1. Field
The present disclosure relates generally to compositions of and methods for making carbonaceous nanomaterials, which are stable in high-salinity, high-temperature conditions. More particularly, the present disclosure relates to zwitterionic compounds that exhibit colloidal stability in high-salinity, high-temperature subterranean environments, such as that of a hydrocarbon-bearing reservoir.
2. Description of the Related Art
Stabilization of nano-sized materials in aqueous environments with high salinities (high ionic strength) is of interest, because such stabilized materials can have great utility in various applications, for example in the petroleum industry. Nanoscale materials can be injected deep into oil reservoirs, and can act as imaging enhancers or act as reporter probes, providing useful information on the state of the reservoirs. Stable nanoscale materials provide the opportunity to improve recovery yields from hydrocarbon-bearing reservoirs. However, the internal environments of oil reservoirs contain high-salinity and high-temperature brines which can readily destabilize nanomaterials injected into them. In addition, certain carbonaceous nanomaterials, such as for example graphene, are hydrophobic and tend to aggregate or flocculate in aqueous solutions, which is undesirable in many applications.
It has been shown that iron oxide nanoparticles wrapped with poly(2-acrylamido-2-methylpropanesulfonate-co-acrylic acid) (also known as poly(AMPS-co-AA)) were effectively stabilized in American Petroleum Institute (API) brine (aqueous 8 wt. % sodium chloride and 2 wt. % calcium chloride) at 90° C. for up to one month. The ionic nature of the polymer successfully imparted electrosteric stabilization and repulsion required to stabilize the nanoparticles against agglomeration in the brine.
Another example also using an ionic polymer was shown to stabilize carbon nanoparticles in API brine. Polyvinyl alcohol (PVA or PVOH) was grafted onto the surface of the nanoparticles and could be sulfated with a chlorosulfonic acid treatment. Lightly sulfated nanoparticles could be stably dispersed in API brine at 100° C. The un-sulfated nanoparticles were not dispersible in the brine. The highly sulfated nanoparticles were not as stable as the lightly sulfated variant forming a suspension of small particulates upon heating.
Highly oxidized graphene oxide (GO) (made with a 5:1 permanganate ratio versus the typical 3:1) formed stable dispersions in aqueous concentrated sodium chloride solutions up to 5 wt. %. The stability of the GO sheets in the brine was ascribed to the presence of a large number of negatively charged groups on the sheet edges that provide sufficient electrostatic repulsion even in a high ionic strength environment. This GO could be used to stabilize oil/water emulsions, but was not examined under harsher conditions including higher ionic strength brine and/or elevated temperatures.
Zwitterionic groups (species containing linked cationic and anionic groups with an overall neutral charge) have excellent brine solubility and stability due to what is referred to as the antipolyelectrolyte effect. This effect causes the chain to expand upon addition of electrolytes which help to stabilize it against agglomeration and destabilization through steric effects (electrosteric stabilization). Such materials have been used in applications including seawater antifouling coatings.
There is a need for compositions of and methods for making carbonaceous nanomaterials that are stable in a suspension at high-salinity and high-temperature conditions.